This invention relates to a system and apparatus for controlling network devices. More particularly, the invention relates to a network-device control system and apparatus for performing control of priority, bandwidth, discard rate and delay in relation the devices that construct a network.
The following functions and features (1) to (3) are currently sought as network requirements:
(1) Quality Assurance
Unification of continuous traffic, such as telephone traffic that is sensitive to delay, and basic business traffic with an IP (Internet Protocol) network of superior cost performance is sought. However, the basic nature of an IP network is best-effort transport of IP packets. In such a best-effort transport environment, an effort is made only to transport arriving packets to the next stage without distinguishing among users or among applications. Packets that cannot be transported (i.e., packets for which buffer overflow has occurred) are discarded as is. Accordingly, in order for a best-effort IP network to accommodate delay-sensitive traffic, it is required that control of traffic priority and assurance of bandwidth based upon the user or application is introduced in an IP network.
(2) Minimum Modification of Existing Network Devices
Replacing terminal devices and network devices (routers, switches, etc.) and installing new software in these devices in order to assure bandwidth and control priority on a network raises the cost of introduction and, hence, is a hindrance to such introduction. Minimizing the modification of existing devices is required in order to solve this problem.
(3) Quality and Priority Control Capable of Dealing with Dynamic Modification of Terminal Devices and Network Devices
Among all devices that construct a network, it will suffice to apply quality and priority control solely to end-to-end devices on the communication path. This communication path is decided in accordance with a predetermined routing protocol based upon the destination address with which communication is performed and the terminal address of the accessing party. However, the destination address and terminal address change constantly depending upon the location of the user and the application utilized. A dynamic quality and priority control method that can deal with such change is sought.
The following two methods have been contemplated for the purpose of performing quality assurance control such as control for assurance of bandwidth or control of priority.
The first method involves statically configuring network devices for the purpose of quality-assurance control. Specifically, control of communication quality with respect to terminal-to-terminal communication is performed by configuring the network devices before hand so that predetermined bandwidth assurance and priority control is attained. This is the most widely utilized approach at present. In order to configure for bandwidth assurance and priority control (i.e., in order to establish control of quality), there are two methods, namely (a) a method referred to as limited configuration method which includes predicting communication that will occur and configuring network devices on this communication path for control of quality in limited fashion, and (b) a method which includes configuring all configurable network devices for control of quality comprehensively without particularly specifying a path.
The second method uses an RSVP (Resource Reservation Protocol) for which control of quality can be configured dynamically. RSVP is a control protocol for reserving resources in the IP layer. According to RSVP, control messages are exchanged between routers that support RSVP and the sender and receiver. The RSVP works to reserve transmission paths and memory resources within an apparatus so that an application can be executed. FIG. 20 is a diagram useful in describing RSVP. A sender 1 sends a receiver 2 a path message that describes the traffic characteristics of the information (content) to be transmitted. The path message is distributed to the receiver 2 by being transferred along a path (routers 3, 4) set up by a predetermined routing protocol. The receiver 2 refers to the content described in the path message and sends a reserve message, which describes the resources requiring reservation, back to the sender 1. If reservation requests from a plurality of receivers are merged and acceptance of a requested bandwidth reservation is possible in a router along the path, bandwidth is secured in accordance with the content of the reservation request and a reserve message is transferred to a router upstream and to the sender 1. If acceptance of a requested bandwidth reservation is impossible, however, the reserve message is discarded and an error message is transmitted to the receiver 1.
The second method based upon RSVP described above makes it possible to control quality dynamically when the user so desires.
However, the first and second methods set forth above do not always satisfy the above-mentioned requirements (1), (2) and (3).
If communication different from that predicted in advance takes place, as when a user makes access from a terminal different from that configured beforehand or when a network device is added on anew, the limited configuration technique according to the first method is such that static quality-control settings will not exist for such communication. This means that the required control of quality cannot be performed. In other words, with the limited configuration method, changes in conditions cannot be dealt with and, as a result, control of quality cannot be realized.
With the other technique available in accordance with the first method, namely the technique through which all configurable network devices are configured for quality control, the user can make access from any terminal whatsoever because all of the terminals will have been configured. However, since settings that support all communication patterns are required for all network devices, the storage area necessary in a network device for the purpose of storing these settings is enormous. (The size of the storage area is proportional to the square of the number of terminals.) Since a network device possesses only a limited storage area, such comprehensive configuring of network devices is difficult. The result is that network communication assumed beforehand undergoes limited configuration.
With the second method, it is assumed that both sending and receive terminals involved in communication and all network devices (routers) on the path along which this communication takes place support RSVP. Consequently, if a network device that does not support RSVP exists in the network, this device cannot undergo any control of quality. If congestion occurs in regard to this network device, even a packet in communication requiring control of quality will be discarded or delayed. The end result is that communication quality cannot be controlled. In order to avoid this problem, components which support RSVP are required for all network devices and it is necessary to increase the storage area and processing capability of each network device.